A numerical model has been developed for struvite-crystallization in a fluidized bed reactor (FBR). For the first time, the flow field and crystal size distribution (CSD) are simultaneously obtained via solving the model that couples computational fluid dynamics (CFD) and population balance equation (PBE). The model was first verified based on the experimental data, and used to explore the influences of operating conditions and reactor geometry. The results showed that the predictions were in good agreement with the experimental observations, giving similar phosphorus removal trend. The predicted supersaturation levels, solid concentrations, and CSDs were found to be strongly dependent on the recycle ratio, pH, and inflow rate. Moreover, the split module was considered better as compared with the traditional integrated module in terms of the supersaturation control. The proposed CFD-PBE modeling framework is thus considered to be a useful tool for performance evaluation and geometry optimization of struvite crystallization. (C) 2017 Elsevier Ltd. All rights reserved.